Adsorption of pyridine of related compounds onto metals.

M. E. ALASSIA; F. A. GUTIERREZ; V. BRUNETTI; O. E. LINAREZ PÉREZ; M. LÓPEZ TEIJELO

San Carlos de Bariloche, Río Negro, Argentina..

Congreso; 13th International Conference on Solid Fims and Surfaces; 2006

Within the last several decades, interactions of small molecules with metal surfaces have attracted much attention, and today, it is one of the most active areas of research. Recently, increasing interest in the use of conjugated molecules for molecular devices such as logic gate transistor, resonant tunnelling diode, etc. has arisen. The self-assembling technique has proved to be a useful method of fabricating such molecular devices [1]. Moreover, funcionalization of metallic surfaces by chemical modification has become an issue in recent years. The preparation of chemically modified electrodes containing immobilized molecules with specific activity for a given reaction is important for the application of these surfaces in electrochemical sensors [2,3]. In this paper, potentiodynamic and potentiostatic methods combined with electrochemical impedance spectroscopy (EIS) measurements as well as ellipsometric characterisation, are used in order to compare the adsorption of aromatic molecules in a wide range of conditions. Cyclic voltammetry allows obtaining the potential regions of stability and desorption of the layers. Preparation of monolayers of mercaptopyridine (N or S-bonded) and isonicotinic acid (N or COO-bonded) on monocrystalline and polycrystalline gold surfaces as well as pyridine and mercaptopyridine on nickel, is reported. The influence of pH of dipping solution and time of dipping in the electrical and optical properties of the adsorbed layers, is analysed. For nickel, different cathodic pre-treatments in acidic and alkaline solutions were applied before the adsorption in order to electroreduce the spontaneous oxide layer The impedance characteristics of these systems are discussed in terms of ideal and non-ideal circuit networks. The elements are associated with electrical analogs of the corresponding physical and chemical processes taking place at the interfaces. The kinetics of electron transfer for redox couples as well as the impedance response were employed in order to obtain information on the compactness of the layers. Ellipsometric results indicate that the cathodic pre-treatments are effective for reducing the nickel oxide as well as indicate the adsorption of pyridine. STM images are employed for obtaining the structural characteristics of the self-assembled layers as well as the changes with potential.